This invention relates to a rubber composition for extrusion and molding and applications thereof.
An ethylene/xcex1-olefin/non-conjugated polyene copolymer rubber such as ethylene/propylene/diene copolymer rubber (EPDM) is widely used for automotive parts, household electric appliance parts, and the like thanks to superior weather ability, heat resistance and ozone resistance.
Among these, materials for sealant or fillers (packing) for automobiles and household electric appliances are the products manufactured by a continuous extrusion molding process.
Requirements for such rubber extrusion composition are continuous feed ability to extruder and no occurrence of crack or tear in a ribbon-like compound preformed prior to an extrusion during its storage.
During extrusion process, cross-sectional area of extrudate should not change, that is, die swell ratio should not vary. Variation in die swell ratio leads to change in cross-sectional shape of glass run or window frame products and may results in lowering of sealing performance and inferior products. Furthermore, in weather strip sponge products, the materials varying in the die swell ratio cause a big problem of uneven foaming since the variation means uneven viscoelastic state in the material.
In addition to these, in extrudate products of EPDM containing carbon black, trouble of foreign matter coming from unknown cause occurs very often. Analysis of a portion of the foreign matter for its cause survey often results in that the portion is composed of the same components to rubber substrate. Mysteriously this trouble naturally disappears, and occurs again sometimes.
On the other hand, there are many products manufactured by molding process in the rubber molding technology. Rubber vibration isolator obtained by injection is one of the products using a rubber composition for molding. Materials for injection are fed as a ribbon-like compound sheeted out using a roll. Tear of the ribbon lowers stability of material feeding and makes continuous production impossible. Such a material may show an abrupt viscosity increase in a feeder of the injection machine and leads to poor flow in a mold after injection. The products molded in such state often had a trouble such as an occurrence of crack during durability test.
Materials used for molding weather strip corner are required to have stable fluidity of the material. Changes of fluidity in each molding cause a serious problem due to poor adhesion at interface with straight parts of weather strip sponge or inferior appearance at joint area.
Fixing roll for copying machine, one of OA rolls, is a foam product having semi conductivity. It often had variation troubles in foaming and electric resistance due to unknown cause.
O-ring product also had troubles of uneven product shrinkage in each molding by unknown cause. Another problem was lowering in mechanical strength of product even with good product appearance.
Analysis of substrate for cause survey often resulted in no specific difference in the substrate composition. These phenomena are troublesome and mysterious because they naturally disappear after a while and the same troubles occur again sometimes.
At present, these trouble is considered to be caused by formation of a physical network originated in carbon black/rubber interface produced in the compound during mixing. That is, this network causes the troubles described above in molding a product.
To solve such problems, adding of polysulfide compounds including sulfur or sulfur compounds as radical scavenger has been disclosed in JP-A-H7-138379.
The addition of such sulfur or sulfur compounds at loading level of about 1.0xc3x9710xe2x88x922 mole per 100 weight parts of polymer in a mixer, however, causes start of cross linking by the presence of zinc oxide (ZnO) contained in the compound and leads to a problem of gelation (chemical burning). Loading level of about 1.0xc3x9710xe2x88x923 mole, {fraction (1/10)} of the above loading level, is safe in view of the burning in a mixer, but has little effect to solve the problems mentioned above.
First object of the invention is to solve such problems described above accompanied with conventional technology, and provide a rubber composition for extrusion to give a ribbon-like compound prepared prior to extrusion having no crack nor tear, stable cross sectional shape of extrudate, and foamed products with little variation in foaming, and also products made of the said rubber composition such as weather strip sponge, high extension seal, glass run channel, window frame and water hose for automobile.
Second object of the invention is to provide a rubber composition for molding to give a compound prepared for injection having no tear phenomenon, superior fluidity in a mold, in addition stable foaming and little variation in foaming in cast sponge, and also products made of the said composition with good surface texture and superior mechanical strength such as rubber vibration isolator, cast sponge, grommet, O-ring, packing, boots, window frame, break piston cup and OA roll products.
The invention includes the following disclosures.
(1) A rubber composition for extrusion comprising 100 weight parts of ethylene/xcex1-olefin/non-conjugated polyene copolymer rubber (A) composed of ethylene, xcex1-olefin having carbon atoms of 3-20 and non-conjugated polyene, and at least 30-300 weight parts of carbon black (B) and 1.0xc3x9710xe2x88x925-5.0xc3x9710xe2x88x923 mol of alkoxysilane compound (C) shown by the following formula (I): 
xe2x80x83wherein, R is an alkyl group having carbon atoms of 1-4 or an alkoxy group having carbon atoms of 1-4, R1 is an alkyl group having carbon atoms of 1-4 or phenyl group, n is 0, 1 or 2, R2 is a bivalence of linear or branched hydrocarbon group having carbon atoms of 1-6, R3 is an arylene group having carbon atoms of 6-12, m and p are 0 or 1 respectively, and m and p are not 0 at a same time, q is 1 or 2, D is xe2x80x94SCN or xe2x80x94SH when q is 1, and xe2x80x94Sxxe2x80x94 when q is 2 (wherein x is an integer of 2-8).
(2) The rubber composition for extrusion according to item 1, wherein the ethylene/xcex1-olefin/non-conjugated polyene copolymer rubber (A) (i) comprises a unit (a) derived from ethylene and a unit (b) derived from xcex1-olefin having carbon atoms of 3-20 in a [(a)/(b)] molar ratio of 50/50-90/10, (ii) has an iodine value of 1-40, and (iii) has an intrinsic viscosity [xcex7] measured in decalin at 135xc2x0 C. of 2.0-4.5 dl/g.
(3) The rubber composition for extrusion according to item 1, wherein an amount of the carbon black (B) is 50-200 weight parts to 100 weight parts of the ethylene/xcex1-olefin/non-conjugated polyene copolymer rubber (A).
(4) The rubber composition for extrusion according to item 1, wherein an amount of the carbon black (B) is 61-200 weight parts to 100 weight parts of the ethylene/xcex1-olefin/non-conjugated polyene copolymer rubber (A).
(5) The rubber composition for extrusion according to item 1, wherein an amount of the carbon black (B) is 70-200 weight parts to 100 weight parts of the ethylene/xcex1-olefin/non-conjugated polyene copolymer rubber (A).
(6) The rubber composition for extrusion according to any one of items 1-5, wherein its apparent activation energy is 20-300 kJ/mol, and a change rate of the apparent activation energy is not higher than 40% even after processing in any rubber processing process.
(7) A rubber composition for extrusion, wherein it does not show any ribbon break nor ribbon crack, and has a change rate in die swell ratio not higher than 5% due to a rise of viscosity in an extruder.
(8) A weather strip sponge product, highly expanded seal product, glass run channel product, window frame product or water hose product for automobile characterized by comprising the rubber composition according to any one of items 1-7.
(9) A process for manufacturing a vulcanized rubber molding product comprising forming the rubber composition according to any one of items 1-7 to an intended shape using an extruder and vulcanizing it.
(10) A rubber composition for molding comprising 100 weight parts of an ethylene/xcex1-olefin/non-conjugated polyene copolymer rubber (A) composed of ethylene, xcex1-olefin having carbon atoms of 3-20 and non-conjugated polyene, and at least 30-300 weight parts of carbon black (B) and 1.0xc3x9710xe2x88x925-5.0xc3x9710xe2x88x923 mol of alkoxysilane compound (C) shown by the following formula (I): 
xe2x80x83wherein, R is an alkyl group having carbon atoms of 1-4 or an alkoxy group having carbon atoms of 1-4, R1 is an alkyl group having carbon atoms of 1-4 or phenyl group, n is 0, 1 or 2, R2 is a bivalence of linear or branched hydrocarbon group having carbon atoms of 1-6, R3 is an arylene group having carbon atoms of 6-12, m and p are 0 or 1 respectively, and m and p are not 0 at a same time, q is 1 or 2, D is xe2x80x94SCN or xe2x80x94SH when q is 1, and xe2x80x94Sxxe2x80x94 when q is 2 (wherein x is an integer of 2-8).
(11) The rubber composition for molding according to item 10, wherein the ethylene/xcex1-olefin/non-conjugated polyene copolymer rubber (A) (i) comprises a unit (a) derived from ethylene and a unit (b) derived from xcex1-olefin having carbon atoms of 3-20 in a [(a)/(b)] molar ratio of 50/50-90/10, (ii) has an iodine value of 1-40, and (iii) has an intrinsic viscosity [xcex7] measured in decalin at 135xc2x0 C. of 0.8-4.5 dl/g.
(12) The rubber composition for molding according to item 10, wherein an amount of the carbon black (B) is 50-200 weight parts to 100 weight parts of the ethylene/xcex1-olefin/non-conjugated polyene copolymer rubber (A).
(13) The rubber composition for molding according to item 10, wherein an amount of the carbon black (B) is 61-200 weight parts to 100 weight parts of the ethylene/xcex1-olefin/non-conjugated polyene copolymer rubber (A).
(14) The rubber composition for molding according to item 10, wherein an amount of the carbon black (B) is 80-200 weight parts to 100 weight parts of the ethylene/xcex1-olefin/non-conjugated polyene copolymer rubber (A).
(15) The rubber composition for molding according to any one of items 10-14, wherein its apparent activation energy is 20-200 kJ/mol, and a change rate change of the apparent activation energy is not higher than 20% even after processing in any rubber processing process.
(16) The rubber composition for molding according to any one of items 10-15, wherein, the composition does not break in a ribbon preformed prior to injection and has a good fluidity in mold which does not vary, and physical properties of the composition after vulcanization do not vary depending on mixing conditions in a preparation of the compound.
(17) A rubber vibration insulator, cast sponge, grommet, O-ring, packing, boots, window frame, break piston cup or OA roll product characterized by comprising the rubber composition according to any one of items 10-16.
(18) A process for manufacturing a vulcanized rubber molding product comprising forming the rubber composition according to any one of items 10-16 to a shape suitable to a molding machine then vulcanizing it.
A rubber composition for extrusion and a rubber composition for molding of the invention comprise 100 weight parts of ethylene/xcex1-olefin/non-conjugated polyene copolymer rubber composed of ethylene, xcex1-olefin having carbon atoms of 3-20 and non-conjugated polyene (A), and at least 30-300 weight parts of carbon black (B) and 1.0xc3x9710xe2x88x925-5.0xc3x9710xe2x88x923 mol of alkoxysilane compound shown by the above described formula (I).
xcex1-Olefin having carbon atoms of 3-20 in ethylene/xcex1-olefin/non-conjugated polyene copolymer rubber (A) used in the invention specifically includes propylene, 1-butene, 1-pentene, 1-hexene, 4-methyl-1-pentene, 1-heptene, 1-octene, 1-nonene, 1-decene, 1-undecene, 1-dodecene, 1-tridecene, 1-tetradecene, 1-pentadecene, 1-hexadecene, 1-heptadecene, 1-octadecene, 1-nonadecene, 1-eicosene, 9-methyl-1-decene, 1-methyl-1-dodecene, 12-ethyl-1-tetradecene and the like. These xcex1-olefins may be used alone or in combination of two or more. Among these xcex1-olefins, those having carbon atoms of 3-8 such as propylene, 1-butene, 4-methyl-1-pentene, 1-hexene and 1-octene are particularly preferable.
In order to obtain a rubber composition providing vulcanized rubber molded products with superior heat aging resistance, strength characteristics, rubber elasticity, low temperature properties and process ability, the ethylene/xcex1-olefin/non-conjugated polyene copolymer rubber (A) preferably comprises (a) an ethylene-derived unit and (b) an xcex1-olefin-derived unit having carbon atoms of 3-20 in [(a)/(b)] molar ratio of 50/50-90/10. The [(a)/(b)] molar ratio described above is preferably 65/35-90/10, more preferably 65/35-85/15 and particularly preferably 65/35-80/20.
As a non-conjugated polyene in the ethylene/xcex1-olefin/non-conjugated polyene copolymer rubber (A), a cyclic or linear non-conjugated polyene may be used.
The cyclic non-conjugated polyene includes, for example, dienes such as methyltetrahydroindene, 5-ethylidene-2-norbornene, 5-methylene-2-norbornene, 5-isopropylidene-2-norbornene, 5-vinyl-2-norbornene, 6-chloromethyl-5-isopropenyl-2-norbornene, dicyclopentadiene and norbornadiene; triene such as 2,3-diisopropylidene-5-norbornene, 2-ethylidene-3-isopropylidene-5-norbornene and 2-propenyl-2,5-norbornadiene.
And as the linear non-conjugated polyene includes, for example, dienes such as 1,4-hexadiene, 3-methyl-1,4-hexadiene, 4-methyl-1,4-hexadiene, 5-methyl-1,4-hexadiene, 4,5-dimethyl-1,4-hexadiene, 6-methyl-1,6-octadiene, 7-methyl-1,6-octadiene, 6-ethyl-1,6-octadiene, 6-propenyl-1,6-octadiene, 6-methyl-1,6-octadiene, 6-methyl-1,6-nonadiene, 7-methyl-1,6-nonadiene, 6-ethyl-1, 6-nonadiene, 7-ethyl-1,6-nonadiene, 6-methyl-1,6-decadiene, 7-methyl-1,6-decadiene, 6-methyl-1,6-undecadiene and 7-methyl-1,6-octadiene; and triene such as 4-ethylidene-1,6-octadiene, 4-ethylidene-7-methyl-1,6-octadiene, 4-ethylidene-7-methyl-1,6-nonadiene, 4-ethylidene-6,7-dimethyl-1,6-octadiene, 4-ethylidene-6,7-dimethyl-1,6-nonadiene, 4-ethylidene-1,6-decadiene, 4-ethylidene-7-methyl-1,6-decadiene, 4-ethylidene-7-methyl-6-propenyl-1,6-octadiene, 4-ethylidene-1,7-nonadiene, 4-ethylidene-8-methyl-1,7-nonadiene, 4-ethylidene-1,7-undecadiene, 4-ethylidene-8-methyl-1,7-undecadiene, 4-ethylidene-7,8-dimethyl-1,7-nonadiene, 4-ethylidene-7,8-dimethyl-1,7-decadiene, 4-ethylidene-7,8-dimethyl-1,7-undecadiene, 7-ethyl-4-ethylidene-8-methyl-1,7-undecadiene, 4-ethylidene-7,8-diethyl-1,7-decadiene, 4-ethylidene-9-methyl-1,8-decadiene, 4-ethylidene-8,9-dimethyl-1,8-decadiene, 4-ethylidene-10-methyl-1,9-undecadiene, 4-ethylidene-9,10-dimethyl-1,9-undecadiene, 4-ethylidene-11-methyl-1,10-dodecadiene, 4-ethylidene-10,11-dimethyl-1,10-dodecadiene and 3,7-dimethyl-1,4,8-decatriene.
These non-conjugated polyenes may be used alone or in combination of two or more.
In view of obtaining a rubber composition having high crosslinking efficiency and capable to provide vulcanized rubber molded products with superior compression set, along with an advantage in cost, iodine value of the ethylene/xcex1-olefin/non-conjugated polyene copolymer rubber (A) is preferably 1-40, more preferably 1-30.
In order to obtain a rubber compound to provide vulcanized rubber molded products with superior strength characteristics, compression set and process ability, intrinsic viscosity [xcex7] of ethylene/xcex1-olefin/non-conjugated polyene copolymer rubber (A), measured in decalin at 135xc2x0 C. is preferably 2.0-4.5 dl/g, more preferably 2.2-4.0 dl/g in the rubber composition for extrusion of the invention, and is preferably 0.8-4.5 dl/g, more preferably 0.9-4.0 dl/g in the rubber composition for molding.
In the rubber composition for extrusion of the invention, carbon black (B) may be used at 30-300 weight parts, preferably at 50-200 weight parts, more preferably at 61-200 weight parts and most preferably at 70-200 weight parts per 100 weight parts of the ethylene/xcex1-olefin/non-conjugated polyene copolymer rubber (A) in order to obtain a rubber composition to be able to provide vulcanized extruded rubber products with sufficient mechanical strength. And in the rubber composition for molding of the invention, carbon black (B) may be used at 30-300 weight parts, preferably at 50-200 weight parts, more preferably at 61-200 weight parts and most preferably at 80-200 weight parts per 100 weight parts of ethylene/xcex1-olefin/non-conjugated polyene copolymer rubber (A) in order to obtain a rubber composition to be able to provide vulcanized molded rubber products with sufficient mechanical strength.
As the carbon black (B), SRF, GPF, FEF, MAF, HAF, ISAF, SAF, FT, MT and the like may be used. In order to obtain a rubber composition to be able to provide vulcanized rubber molded products with superior mechanical strength and surface texture of products, specific surface area by nitrogen absorption of carbon black (B) is preferably 10-100 m2 /g.
In the invention, an alkoxysilane compound (C) shown by the formula (I) described above is compounded to reduce a change rate in activation energy of a compound and suppress the formation of physical network originating from carbon black/polymer interface in the compound during mixing. In order to obtain sufficient effects and maintain vulcanization rate and rubber elasticity, loading level of the alkoxysilane compound (C) should be 1.0xc3x9710xe2x88x925-5.0xc3x9710xe2x88x923 mole, preferably 1.0xc3x9710xe2x88x924-4.0xc3x9710xe2x88x923 mole and further preferably 1.0xc3x9710xe2x88x924-2.1xc3x9710xe2x88x923 mole per 100 weight parts of the ethylene/xcex1-olefin/non-conjugated polyene copolymer rubber (A).
Alkoxysilane compound (C) may be used as an impregnated form into calcium carbonate or carbon black (B) in advance.
In the formula (I) described above, alkyl group having carbon atoms of 1-4 shown as R or R1 includes, for example, methyl, ethyl, n-propenyl, isopropyl, n-buthyl, isobutyl, sec-butyl and tert-butyl. Alkoxy group having carbon atoms of 1-4 shown as R includes, for example, methoxy, ethoxy, propoxy, isopropoxy, n-butoxy, isobutoxy, sec-butoxy and tert-butoxy. Linear or branched bivalent hydrocarbon group having carbon atoms of 1-6 shown as R2 includes, for example, alkylene group such as methylene, dimethylmethylene, ethylene, dimethylethylene, trimethylene, tetramethylene, 1,2-cyclohexylene and 1,4-cyclohexylene; alkylidene group such as cyclohexylidene; arylalkylene group such as diphenylmethylene and diphenylethylene. Arylene group having carbon atoms of 6-12 shown as R3 includes, for example, phenylene, naphthylene and biphenylylene.
Typical examples of the alkoxysilane compound (C) shown in the formula (I) described above includes bis-3-(trimethoxysilyl) propyltetrasulfane [(CH3O)3 Sixe2x80x94(CH2)3xe2x80x94S4xe2x80x94(CH2)3xe2x80x94Si(OCH3)3], bis-3-(triethoxysilyl)propyltetrasulfane [(C2H5O)3Sixe2x80x94(CH2)3xe2x80x94S4xe2x80x94(CH2)3xe2x80x94Si (OC2H5)3] and bis-3-(tripropoxysilyl)propyltetrasulfane [(C3H7O)3Sixe2x80x94(CH2)3xe2x80x94S4xe2x80x94(CH2)3xe2x80x94Si(OC3H7)3].
A rubber composition for extrusion and molding of the invention may be compounded with additives known in the art other than carbon black (B), such as rubber reinforcing agents, inorganic fillers, softening agents, antioxidants, processing aids, foaming agents, co-foaming agents, vulcanization accelerators, organic peroxides, vulcanization promoters, colorants, dispersing agents, flame retardants and the like, at loading level not impairing purposes of the invention, depending on intended applications of vulcanized products, etc.
The rubber reinforcing agents described above have an enhancing effect on mechanical properties such as tensile strength, tear strength and wear resistance and the like. Typical examples of such rubber reinforcing agents include fine powder of silicic acid, silica and the like. These may be pretreated with silane coupling agents.
Typical examples of silica are fumed silica and precipitated silica and the like. These silica may be applied with surface treatment by reactive silane such as mercaptosilane, aminosilane, hexamethyldisilazane, chlorosilane and alkoxylsilane or siloxane of low molecular weight.
Types and loading levels of these rubber reinforcing agents may be suitably selected depending on applications, and maximum loading levels, except for carbon black (B), are generally 150 weight parts, preferably 100 weight parts per 100 weight parts of the ethylene a xcex1-olefin/non-conjugated polyene copolymer rubber (A).
Typical inorganic fillers described above include light calcium carbonate, ground calcium carbonate, talc, clay and the like.
Types and loading levels of these inorganic fillers may be suitably selected depending on applications and maximum loading levels are generally 300 weight parts, preferably 200 weight parts per 100 weight parts of the ethylene/xcex1-olefin/non-conjugated polyene copolymer rubber (A).
As the softening agents described above, those generally used for rubber may be used. They include, typically, petroleum based softening agents such as process oil, lubricating oil, paraffin oil, liquid paraffin, petroleum asphalt and vaseline; coal tar based softening agents such as coal tar and coal tar pitch; fatty oil based softening agents such as castor oil, linseed oil, rapeseed oil, soybean oil and coconut oil; tall oil; rubber substitute (factice); waxes such as beeswax, carnauba wax and lanolin; fatty acids and salts thereof such as ricinolic acid, palmitic acid, stearic acid, barium stearate, calcium stearate and zinc laurate; naphthenic acid; pine oil, rosin or derivatives thereof; synthetic polymer materials such as terpene resin, petroleum based resin, atactic polypropylene and coumarone-indene resin; ester based softening agents such as dioctyl phthalate, dioctyl adipate and dioctyl sebacate; microcrystalline wax, liquid polybutadiene, modified liquid polybutadiene, liquid Thiokol, hydrocarbon based synthetic lubricating oil and the like. Among these, petroleum based softening agents, in particular, process oil is suitably used. Loading levels of these softening agents may be selected depending on applications of vulcanized products.
The antioxidants described above include, for example, amine based, hindered phenol based or sulfur based antioxidant and the like, and may be used in the range of loading level not to impair purposes of the invention. Amine based antioxidants include diphenylamine, phenylenediamine and the like. Sulfur based antioxidants include those usually adopted in rubber.
As the processing aids described above, those generally adopted in rubber processing may be used. Typically, higher fatty acids such as linoleic acid, ricinolic acid, stearic acis, palmitic acid and laulic acid; salts of higher fatty acids such as barium stearate, zinc stearate and calcium stearate; esters of higher fatty acids described above and the like are included. These processing aids may be used at not more than 10 weight parts, preferably not more than 5 weight parts per 100 weight parts of the ethylene/xcex1-olefin/non-conjugated polyene copolymer rubber (A), however, it is desirable to suitably determine an optimal amount depending on required physical properties.
Foaming agents typically include inorganic foaming agents such as sodium bicarbonate, sodium carbonate, ammonium bicarbonate, ammonium carbonate and ammonium nitrite; nitroso compounds such as N,Nxe2x80x2-dimethyl-N,Nxe2x80x2-dinitrosoterephthalamide and N,Nxe2x80x2-dinitrosopentamethylenetetramine (DPT); azo compounds such as azodicarbonamide (ADCA), azobisisobutyronitrile (AZBN), azobiscyclohexylnitrile, azodiaminobenzene and barium azodicarboxylate; sulfonylhydrazide compounds such as benzenesulfonylhydrazide (BSH), toluenesulfonylhydrazide (TSH), p,pxe2x80x2-oxybis (benzenesulfonylhydrazide) (OBSH) and diphenylsulfone-3,3xe2x80x2-disulfonylhydrazide; azide compounds such as calcium azide, 4,4xe2x80x2-diphenyldisulfonylazide and p-toluenesulfonylazide.
These foaming agents may generally be used at the ratio of 0.5-30 weight parts, preferably 1-20 weight parts per 100 weight parts of the ethylene/xcex1-olefin/non-conjugated polyene copolymer rubber (A). Use of the foaming agents at the ratio described above enables manufacturing of a foamed product with apparent specific gravity of 0.03-0.8 g/cm3 for the rubber composition for extrusion of the invention, and a foamed product with apparent specific gravity of 0.1-0.8 g/cm3 for the rubber composition for molding of the invention. However, it is desirable to determine suitably an optimal amount depending on required physical properties.
Co-foaming agents may be used in combination with the foaming agents, if necessary. The co-foaming agents act to lower decomposition temperature, accelerate decomposition of the foaming agents and achieve even foaming. Such co-foaming agents include, for example, organic acids such as salicylic acid, phthalic acid, stearic acid and oxalic acid, urea and derivatives thereof. These co-foaming agents may generally be used at the ratio of 0.01-10 weight parts, preferably 0.1-5 weight parts per 100 weight parts of the ethylene/xcex1-olefin/non-conjugated polyene copolymer rubber (A), however, it is desirable to determine suitably an optimal amount depending on required properties.
In addition, another rubber known in the arts may be used by blending with the crosslinkable rubber composition of the invention, so long as not to impair objectives of the invention.
Such another rubber includes natural rubber (NR), isoprene based rubber such as polyisoprene rubber (IR) and conjugated diene based rubber such as polybutadiene rubber (BR), styrene-butadiene rubber (SBR), acrylonitrile-butadiene rubber (NBR) and chloroprene rubber (CR).
Vulcanization agents used for vulcanization include sulfur and sulfur compounds. Typical sulfur includes, powder sulfur, precipitated sulfur, colloidal sulfur, surface treated sulfur, insoluble sulfur and the like. Typical sulfur compounds include sulfur chloride, sulfur dichloride, polymeric polysulfide and sulfur compounds to vulcanize a composition by generating active sulfur at vulcanizationtemperature such as morpholine disulfide, alkylphenol disulfide, tetramethylthiuram disulfide, dipentamethylenethiuram tetrasulfide, Selenium dimethyldithiocarbamate and the like. Sulfur is preferable among these. Sulfur and sulfur compounds may generally be used at the ratio of 0.1-10 weight parts, preferably 0.5-5 weight parts per 100 weight parts of the copolymer rubber (A) described above.
In using sulfur or sulfur compounds as vulcanization agents, combined use of vulcanization accelerators is preferable. Typical vulcanization accelerators include sulfenamide compounds such as N-cyclohexyl-2-benzothiazolesulfenamide (CBS), N-oxydiethylene glycol-2-benzothiazolesulfenamide (OBS), N-t-butyl-2-benzothiazolesulfenamide (BBS) and N,N-diisopropyl-2-benzothiazolesulfenamide; thiazole compounds such as 2-mercaptobenzothiazole (MBT), 2-(2,4-dinitrophenyl)mercaptobenzothiazole, 2-(4-morpholinodithio)benzothiazole, 2-(2,6-diethyl-4-morpholinothio)benzothiazole and dibenzothiazyldisulfide; guanidine compounds such as diphenylguanidine (DPG), triphenylguanidine, diorthotolylguanidine (DOTG), orthotolylbiguanide and diphenylguanidine phthalate; aldehyde amine or aldehyde-ammonium type compounds such as acetaldehyde-aniline condensed compounds, butylaldehyde-aniline condensed compounds, hexamethylenetetramine (H) and acetaldehyde ammonia; imidazoline compounds such as 2-mercaptoimidazoline; thiourea compounds such as thiocarbanilide, diethylthiourea (EUR), dibutylthiburea, trimethylthiourea and diorthotolylthiourea; thiuram compounds such as tetramethylthiuram monosulfide (TMTM), tetramethylthiuram disulfide (TMTD), tetraethylthiuram monosulfide, tetrabutylthiuram disulfide, tetrakis(2-ethylhexyl)thiuram disulfide (TOT) and dipentamethylenetetrathiuram sulfide (TRA); salts of dithiocarbamic acid such as zinc dimethyldithiocarbamate, zinc diethyldithiocarbamate, zinc di-n-butyldithiocarbamate, zinc ethylphenyldithiocarbamate, zinc butylphenyldithiocarbamate, sodium dimethyldithiocarbamate, selenium dimethyldithiocarbamate and tellurium dimethyldithiocarbamate; xanthate such as zinc dibutylxanthate; compounds such as zinc white (zinc oxide); and the like. These vulcanization accelerators may generally be used at the ratio of 0.1-20 weight parts, preferably 0.2-10 weight parts per 100 weight parts of the copolymer rubber (A) described above.
The rubber composition of the invention may be prepared by mixing ethylene/xcex1-olefin/non-conjugated polyene copolymer rubber (A), carbon black (B), alkoxysilane compound (C) and additives such as rubber reinforcing agents, inorganic fillers and softening agents using an internal mixer (closed type mixer) such as Bumbury""s mixer and kneader at 80-170xc2x0 C. for 2-20 min., followed by additional mixing of sulfur together with optional vulcanization accelerators, vulcanization aids, foaming agents and co-foaming agents using a roll such as open role or kneader at roll temperature of 40-80xc2x0 C. for 5-30 min., then sheeting out.
The rubber composition for extrusion of the invention prepared as described above may be shaped as intended by an extruder and vulcanized at 140-270xc2x0 C. for 1-30 min. simultaneously with the extrusion or by introducing the extrudate into a vulcanization chamber. Vulcanization process is generally carried out continuously. As a heating method in the vulcanization chamber, a heating measure such as hot air, fluidized bed of glass beads, molten salt bath (LCM), PCM (Powder Curing Medium or Powder Curing Method), UHF (ultra high frequency microwave), steam and the like may be used.
And the rubber composition for molding of the invention prepared as described above may be shaped suitably for a molding machine for molded products. Sheet-like compound is prepared using a roll, etc. in advance for a compression molding and vulcanization machine. In an injection, ribbon-like compound is sheet out roll and stored until molding. In a transfer molding of cast sponge products, ball-like compound is prepared in advance. The compounds thus prepared may be vulcanized by heating at 140-270xc2x0 C. for 1-30 min.
The inventors, after thorough investigation on the problems accompanied with conventional technology, clarified that the cause is changes in compound viscosity depending on mixing conditions in the ethylene/xcex1-olefin/non-conjugated polyene copolymer rubber system loaded with carbon black. The inventors presumed that the cause is formation of a network between interfaces of carbon black/polymer (FIG. 1) since this phenomenon is specified to the compound system loaded with carbon black. The larger the specific surface area of carbon black is and the higher the loading level of carbon black is, the easier this network tends to be formed. The network also tends to be formed at higher mixing temperature when mixing time is longer. Formation of such network or use of material with generation of origins of such network at carbon black/polymer interfaces results in an abrupt increase in viscosity in an extruder or a mold. It then impairs the production of extrudate due to change in cross sectional shape, that is, change in die swell ratio in the composition for extrusion, and causes fluctuation of fluidity, change in product shrinkage or poor foaming in the composition for molding. Furthermore, in any case of the rubber composition for extrusion and molding, a ribbon crack phenomenon occurs, that is, cracks occur at bending part of the compound during storage after mixing in a mixer and forming to a ribbon-like compound, and thus leads to a serious problem like a lowering in continuous productivity.
For a rubber composition for extrusion and molding, it is very important not to have such viscosity increase which is closely relating to inferior product ratio.
For a further precise explanation, this network means structural change occurred inside a compound.
As an index to express the structural change in the compound by mixing, an apparent activation energy is used in the Examples described hereinafter. The activation energy is obtained from a temperature dependency of viscosity, and determined by quality of the polymer to be used, compounding of carbon black and the like and loading levels of these materials. Its value becomes smaller when the network (physical structural change) described above is formed.
The inventors, after a thorough investigation, found that the apparent activation energy of the rubber composition for extrusion should be 20-300 kJ/mole, preferably 30-250 kJ/mole, and more preferably 30-200 kJ/mole, and also that a change rate between the apparent activation energy after mixing by rubber mixer and that of right after extrusion in the next process should be not higher than 40%, preferably not higher than 30%, and more preferably not higher than 25% to solve the problems associated with conventional technology. Similarly, the inventors found that the apparent activation energy of the rubber composition for molding should be 20-200 kJ/mole, preferably 30-150 kJ/mole, and more preferably 30-120 kJ/mole, and also that a change rate between the apparent activation energy after mixing by rubber and that of sheet-like, ribbon-like or ball-like compound in the case of transfer molding should be not higher than 20%, preferably not higher than 15%, and further preferably not higher than 10% to solve the problems associated with conventional technology.
Here, the apparent activation energy can not be measured in the presence of vulcanization agents because vulcanization proceeds during the measurement. Therefore, it was evaluated using the compounds without the vulcanization agents in the Examples described hereinafter. In ordinary production, ribbon-like compounds, materials extruded from extruder or compounds before molding contain the vulcanization agents. Results obtained by measurement of the apparent activation energy to grasp and control the effects of the invention do not change by the presence or absence of the vulcanization agents.
Based on these consideration, in preparation of the rubber composition for extrusion of the invention, it is desirable to mix under such conditions that the apparent activation energy of compound (1) obtained by the mixing procedure according to JIS K6395 with an open roll of 8 inch xcfx86 becomes generally 20-300 kJ/mole, preferably 30-250 kJ/mole, and further preferably 30-200 kJ/mole. Furthermore, it is desirable to mix under such conditions that the apparent activation energy of compound (2) obtained by mixing with a mixer usually used in the rubber industry and then extruding with a extruder for rubber becomes 20-300 kJ/mole and the change rate (%) of the activation energy expressed by the following formula:
[1xe2x88x92(apparent activation energy of compound (2))/(apparent activation energy of compound (1))]xc3x97100
becomes generally not higher than 40%, preferably not higher than 30%, and more preferably not higher than 20% as the result of the reaction between carbon black (B) and alkoxysilane compound (C) (silane coupling agent).
And also, in preparation of the rubber composition for molding of the invention, it is desirable to mix under such conditions that the apparent activation energy of compound (1) obtained by the mixing procedure according to JIS K6395 with an open roll of 8 inch xcfx86 becomes generally 20-200 kJ/mole, preferably 30-150 kJ/mole, and further preferably 30-120 kJ/mole. Furthermore, it is desirable to mix under such conditions that the apparent activation energy of compound (2) obtained by mixing with a mixer usually used in the rubber industry and then forming to sheet-like for molding or ribbon-like for injection becomes 20-200 kJ/mole and the change rate (%) of the activation energy expressed by the following formula:
[1xe2x88x92(apparent activation energy of compound (2))/(apparent activation energy of compound (1))]xc3x97100
becomes generally not higher than 20%, preferably not higher than 15%, and more preferably not higher than 10% as a result of the reaction between carbon black (B) and alkoxysilane compound (C) (silane coupling agent).
Under coexistence of zinc oxide and silane coupling agent, the silane coupling agent react with zinc oxide first resulting in decrease of the silane coupling agent to be combined with carbon black surface, increased change rate of the activation energy of the material, and lowering of the effect of the silane coupling agent. That is, the change rate of the activation energy of material becomes an important parameter to obtain the effect of the silane coupling agent.
In the Examples described hereinbelow, reasons for adopting the activation energy of compounds mixed with an open roll of 8 inch xcfx86 as the standard are: No formation of the network described above in a compound due to low mixing temperature (temperatures of front roll/back roll=50xc2x0 C./50xc2x0 C.), and expectable stabilization of radicals generated by polymer chain scission induced by shear due to presence of oxygen, along with possible better dispersion of carbon black, etc. compared with other mixers. The network among carbon black/polymer interfaces discussed in the invention is hardly formed in an open state (in the presence of oxygen) and at mild mixing temperature. In order to quantify and control amount of the network formed in a closed type mixer generally used in mixing process in the rubber industry, the state of network is quantified using the apparent activation energy as a standard value. Larger change rate in apparent activation energy by mixing means more network formation in a mixer and gives the problems of ribbon crack or tear. Furthermore, even if such phenomena do not happen in a mixer, the compound with origin of network formation gives abrupt increase in viscosity and thus resulting in fluctuation of fluidity or extrusion out put, changes in product cross sectional shape or shrinkage and inferior foaming.
Reasons for the suppression effect of alkoxysilane (C) on network formation is rapid reaction of silanol functional group in its chemical structure with active species (carboxyl group, lactone, hydroxyl group, ketone group and phenol group) at carbon black surface and rapidly covering the surface during reaction, along with stabilization effect of polysulfide group on the origin points (at carbon black/polymer interface) for network formation among the interfaces.
That is, alkoxysilane (C), even in very small amount, effectively and rapidly disperses to carbon black/polymer interfaces, cause points for viscosity increase to raise the problem in extrusion and molding of a compound material, and stabilizes origin sites of network formation and thus suppresses the network formation. Since this effect is obtained with very small amount there is no fear of burning in mixing, a problem of polysulfide compounds such as sulfur in conventional technology described above.
A vulcanized rubber product thus obtained are used for sponge weather strip, seal products with high extension, glass run channel, window frame and water hose for automobile, in the rubber composition for extrusion of the invention, whereas rubber vibration isolator, cast sponge, grommet, O-ring, packing, boots, window frame, break piston cup and OA roll, in the rubber composition for molding of the invention.